scholarly journals Modelling size segregation of granular materials: the roles of segregation, advection and diffusion

2014 ◽  
Vol 741 ◽  
pp. 252-279 ◽  
Author(s):  
Yi Fan ◽  
Conor P. Schlick ◽  
Paul B. Umbanhowar ◽  
Julio M. Ottino ◽  
Richard M. Lueptow
Keyword(s):  
Granular Materials ◽  
Dimensionless Parameter ◽  
System Size ◽  
Quantitative Agreement ◽  
Particle Sizes ◽  
Control Parameters ◽  
Size Segregation ◽  
Particle Segregation ◽  
Kinematic Measures ◽  
And Diffusion

AbstractPredicting segregation of granular materials composed of different-sized particles is a challenging problem. In this paper, we develop and implement a theoretical model that captures the interplay between advection, segregation and diffusion in size bidisperse granular materials. The fluxes associated with these three driving factors depend on the underlying kinematics, whose characteristics play key roles in determining particle segregation configurations. Unlike previous models for segregation, our model uses parameters based on kinematic measures from discrete element method simulations instead of arbitrarily adjustable fitting parameters, and it achieves excellent quantitative agreement with both experimental and simulation results when applied to quasi-two-dimensional bounded heaps. The model yields two dimensionless control parameters, both of which are only functions of control parameters (feed rate, particle sizes, and system size) and kinematic parameters (diffusion coefficient, flowing layer depth, and percolation velocity). The Péclet number, $\mathit{Pe}$, captures the interplay of advection and diffusion, and the second dimensionless parameter, $\Lambda $, describes the interplay between segregation and advection. A parametric study of $\Lambda $ and $\mathit{Pe}$ demonstrates how the particle segregation configuration depends on the interplay of advection, segregation and diffusion. The model can be readily adapted to other flow geometries.

Molecular Dynamics Study of Cohesionless Granular Materials: Size Segregation by Shaking

1993 ◽  
Vol 07 (09n10) ◽  
pp. 1865-1872 ◽  
Author(s):  
Toshiya OHTSUKI ◽  
Yoshikazu TAKEMOTO ◽  
Tatsuo HATA ◽  
Shigeki KAWAI ◽  
Akihisa HAYASHI
Keyword(s):  
Molecular Dynamics ◽  
Steady State ◽  
Specific Gravity ◽  
Pressure Gradient ◽  
Granular Materials ◽  
Buoyancy Force ◽  
Temporal Evolution ◽  
Particle Radius ◽  
Size Segregation ◽  
Increasing Function

The Molecular Dynamics technique is used to investigate size segregation by shaking in cohesionless granular materials. Temporal evolution of the height h of the tagged particle with different size and mass is measured for various values of the particle radius and specific gravity. It becomes evident that h approaches the steady state value h∞ independent of initial positions. There exists a threshold of the specific gravity of the particle. Below the threshold, h∞ is an increasing function of the particle size, whereas above it, h∞ decreases with increasing the particle radius. The relaxation time τ towards the steady state is calculated and its dependence on the particle radius and specific gravity is clarified. The pressure gradient of pure systems is also measured and turned out to be almost constant. This suggests that the buoyancy force due to the pressure gradient is not responsible to h∞.

scholarly journals Dynamically structured bubbling in vibrated gas-fluidized granular materials

2021 ◽  
Vol 118 (35) ◽  
pp. e2108647118
Author(s):  
Qiang Guo ◽  
Yuxuan Zhang ◽  
Azin Padash ◽  
Kenan Xi ◽  
Thomas M. Kovar ◽  
...  
Keyword(s):  
Resonant Frequency ◽  
Granular Materials ◽  
Fluidized Beds ◽  
Gas Flow ◽  
Scale Up ◽  
Clean Energy ◽  
System Size ◽  
Optimal Operation ◽  
Constitutive Relationship ◽  
Energy Processes

The dynamics of granular materials are critical to many natural and industrial processes; granular motion is often strikingly similar to flow in conventional liquids. Food, pharmaceutical, and clean energy processes utilize bubbling fluidized beds, systems in which gas is flowed upward through granular particles, suspending the particles in a liquid-like state through which gas voids or bubbles rise. Here, we demonstrate that vibrating these systems at a resonant frequency can transform the normally chaotic motion of these bubbles into a dynamically structured configuration, creating reproducible, controlled motion of particles and gas. The resonant frequency is independent of particle properties and system size, and a simple harmonic oscillator model captures this frequency. Discrete particle simulations show that bubble structuring forms because of rapid, local transitions between solid-like and fluid-like behavior in the grains induced by vibration. Existing continuum models for gas–solid flows struggle to capture these fluid–solid transitions and thus cannot predict the bubble structuring. We propose a constitutive relationship for solids stress that predicts fluid–solid transitions and hence captures the experimental structured bubbling patterns. Similar structuring has been observed by oscillating gas flow in bubbling fluidized beds. We show that vibrating bubbling fluidized beds can produce a more ordered structure, particularly as system size is increased. The scalable structure and continuum model proposed here provide the potential to address major issues with scale-up and optimal operation, which currently limit the use of bubbling fluidized beds in existing and emerging technologies.

Application of simulation technologies in the analysis of granular material behaviour during transport and storage

2005 ◽  
Vol 219 (1) ◽  
pp. 43-52 ◽  
Author(s):  
P Chapelle ◽  
N Christakis ◽  
J Wang ◽  
N Strusevich ◽  
M. K. Patel ◽  
...  
Keyword(s):  
Granular Material ◽  
Granular Materials ◽  
Large Scale ◽  
Computational Models ◽  
Research Programme ◽  
Size Segregation ◽  
Materials Handling ◽  
Simulation Tools ◽  
And Storage

Problems in the preservation of the quality of granular material products are complex and arise from a series of sources during transport and storage. In either designing a new plant or, more likely, analysing problems that give rise to product quality degradation in existing operations, practical measurement and simulation tools and technologies are required to support the process engineer. These technologies are required to help in both identifying the source of such problems and then designing them out. As part of a major research programme on quality in particulate manufacturing computational models have been developed for segregation in silos, degradation in pneumatic conveyors, and the development of caking during storage, which use where possible, micro-mechanical relationships to characterize the behaviour of granular materials. The objective of the work presented here is to demonstrate the use of these computational models of unit processes involved in the analysis of large-scale processes involving the handling of granular materials. This paper presents a set of simulations of a complete large-scale granular materials handling operation, involving the discharge of the materials from a silo, its transport through a dilute-phase pneumatic conveyor, and the material storage in a big bag under varying environmental temperature and humidity conditions. Conclusions are drawn on the capability of the computational models to represent key granular processes, including particle size segregation, degradation, and moisture migration caking.

Large-scale flume modelling of segregation processes in debris flows

2020 ◽  
Author(s):  
Julia Kimball ◽  
W Andrew Take
Keyword(s):  
Debris Flows ◽  
Large Scale ◽  
Multicomponent Mixture ◽  
Granular Flows ◽  
Particle Sizes ◽  
Deposit Morphology ◽  
Multicomponent Mixtures ◽  
Particle Segregation ◽  
Experimental Strategies ◽  
Landslide Deposit

<p>Debris flows are powerful natural hazards posing risk to life, infrastructure, and property.  Understanding the particle scale interactions in these flows is a key component in the development of models to predict the mobility, distal reach, and hazard posed by a given event. In this study we focus on the process of segregation in debris flows, using a large-scale landslide flume to explore segregation in mixtures of 25 mm, 12 mm, 6 mm, and 3 mm diameter particle sizes. Sample volumes, consisting of a multicomponent mixture of materials, up to 1 m<sup>3</sup> in size are released at the top of a 6.8 m long, 2.1 m wide slope, inclined at 30 degrees to the horizontal to initiate flow. Subsequent analysis is completed to determine the extent of vertical and longitudinal segregation of the post-landslide deposit morphology. A range of experimental strategies are explored to provide quantitative measures of particle segregation. Particle size is identified via image analysis and various techniques are applied for the longitudinal sectioning of the deposit, using measurements of segregation at the sidewall of the transparent flume, contrasted with planes measured from within the centre of the deposit. Further, replicate experiments are shown to quantify the probabilistic variation in segregation for multicomponent mixtures of dry granular flows, as well as initially saturated granular flows, to explore the effect of pore fluid on segregation processes.</p>

scholarly journals Jamming, plasticity and diffusion in dense granular materials

PAMM ◽  
2007 ◽  
Vol 7 (1) ◽  
pp. 1090603-1090604
Author(s):  
R.P. Behringer
Keyword(s):  
Granular Materials ◽  
And Diffusion

scholarly journals Size segregation of intruders in perpetual granular avalanches

2017 ◽  
Vol 825 ◽  
pp. 502-514 ◽  
Author(s):  
Benjy Marks ◽  
Jon Alm Eriksen ◽  
Guillaume Dumazer ◽  
Bjørnar Sandnes ◽  
Knut Jørgen Måløy
Keyword(s):  
Fixed Point ◽  
Continuum Theory ◽  
Particle Sizes ◽  
Size Segregation ◽  
Uniform Size ◽  
Single Location ◽  
Two Dimensional Flow ◽  
Fixed Point Attractor ◽  
Experimental Findings ◽  
The Continuum

Granular flows such as landslides, debris flows and avalanches are systems of particles with a large range of particle sizes that typically segregate while flowing. The physical mechanisms responsible for this process, however, are still poorly understood, and there is no predictive framework for ascertaining the segregation behaviour of a given system of particles. Here, we provide experimental evidence of individual large intruder particles being attracted to a fixed point in a dry two-dimensional flow of particles of otherwise uniform size. A continuum theory is proposed which captures this effect using only a single fitting parameter that describes the rate of segregation, given knowledge of the bulk flow field. Predictions of the continuum theory are compared with the experimental findings, both for the typical location and velocity field of a range of intruder sizes. For large intruder particle sizes, the continuum model successfully predicts that a fixed point attractor will form, where intruders are drawn to a single location.

Dynamics of size segregation of granular materials by shaking

1998 ◽  
Vol 20 (9) ◽  
pp. 1443-1448 ◽  
Author(s):  
Zhu Jiongming ◽  
Zhou Binglu ◽  
Wang Bin
Keyword(s):  
Granular Materials ◽  
Size Segregation

Dynamics of Granular Compaction

1997 ◽  
Vol 07 (05) ◽  
pp. 1159-1165 ◽  
Author(s):  
Hisao Hayakawa ◽  
Daniel C. Hong
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Granular Materials ◽  
Hard Sphere ◽  
Dimensionless Parameter ◽  
Preliminary Investigation ◽  
State Density ◽  
Dynamic Evolution ◽  
Initial State ◽  
Granular Compaction

We investigate the way the disordered granular materials organize themselves in a vibrating bed, the intensity of which is given by the dimensionless parameter Γ. Based on the recognition that an assembly of mono-disperse and cohesionless granular materials is a collection of spinless hard sphere Fermions, we first demonstrate that the time averaged steady state density profile for weak excitation with Γ ≈ 1 is given by the Fermi distribution. This is consistent with the observed experimental data and the results of Molecular dynamics. We then present a dynamic model to study the dynamics of granular compaction, namely the dynamic evolution of the initial state ultimately relaxing toward this steady state. Our preliminary investigation reveals that the relaxation is exponential, which is not inconsistent with the available experimental data for low Γ.

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